The present invention relates generally to the field of
instruments and relates more particularly to endodontic reamers and files used for cleaning and shaping root canals.
In order to remove decayed, injured or dead tissue from the root canal of a tooth, an endodontist will first drill into the tooth to locate the root canal and thereafter use instruments of small diameter, such as reamers and files, to remove the decayed, injured or dead tissue from the canal. The goal of tissue removal with the instrument is to produce a funnel-shaped canal, with the smaller end at the apical foramin, so as to provide the canal with a desirable form for filling. Since root canals are not necessarily straight, the instrument must be able to follow a curved path as it is moved through the canal for purposes of removing the tissue. Therefore, the instrument must be flexible yet possess sufficient strength so that it is not easily broken when moved through a root canal.
Commonly, both files and reamers have flutes which spiral along a portion of the instrument length, and whether the instrument is a file or a reamer is determined by the pitch of the flutes. A greater pitch enables the instrument to cut better in a rotary mode, hence a reamer, and a lesser pitch enables the pitch to cut better in the reciprocating mode, hence a file. During a cleaning and shaping operation performed with such a file or reamer, the instrument is normally rotated and moved into and out of the root canal along the longitudinal axis of the instrument. Therefore, even during rotational movement of a reamer through a canal, the instrument is commonly reciprocated to a degree to effect the desired cut. Similarly, a file is commonly rotated slightly as it is reciprocated longitudinally.
In order that the instrument cut into root canal tissue as it is rotated and moved longitudinally, relatively high torsion forces must be typically applied to the instrument. This translates into relatively high torsional loads on the instrument and may lead to torsional failure of the instrument. In addition, the curved path of common root canals which requires that the instrument concurrently be subjected to bending and torsional loads as it is moved along the canal increases the likelihood of torsional failure.
Accordingly, it is an object of the present invention to provide an improved endodontic instrument, such as a reamer or file, which requires that only a relatively small amount of torsion force be applied in order that the instrument be simultaneously rotated and moved along its longitudinal axis through a root canal.
Another object of the present invention is to provide such an instrument which provides a relatively clean cut when moved in cutting relationship with root canal tissue.
More particularly, the present invention provides an endodontic instrument, such as a reamer or file, having an elongated shank having a working, or cutting, portion which extends along a section of the length of the shank and includes a leading end. The shank also includes a pilot attached to the working portion at the leading end thereof so as to be arranged coaxially with the working portion and which is smaller in diameter than the diameter of the working portion at the leading end. The working portion includes at least one continuous helical flute which spirals along the length of the working portion and extends between adjacent flutes and further includes at least one lip adjacent the pilot which has a cutting edge which generally lies in a radial plane of the shank. Each flute which spirals along the length of the working portion terminates at the cutting edge of a corresponding lip so that as the instrument is moved longitudinally through a root canal, root canal tissue disposed to one side of the pilot is exposed to the cutting edge of the working portion.
A more complete understanding of the present invention will be had by reference to the specification and accompanying drawings wherein like numerals refer to like parts throughout.